The present invention relates, in general, to chemical mechanical planarization (CMP) systems, and more particularly, to a translation mechanism.
In general, chemical mechanical planarization (CMP) is used to remove material or a global film from a processed side of a semiconductor wafer. Ideally, a uniform amount of material is removed across the semiconductor wafer leaving a highly planar surface on which to continue wafer processing. Any non-uniformity in the polishing process may result in a loss of yield or long term device reliability problems. Uniformity is the measure of variation in surface height across a semiconductor wafer. Some common types of chemical mechanical planarization processes in the semiconductor industry are used to remove oxides, polysilicon, tungsten, and copper.
The future of chemical mechanical planarization is challenged by the fact that device/interconnect geometries are decreasing to a level that requires greater control and uniformity of the planarization process, both of which are difficult to achieve. The complexity of the planarization problem is being exacerbated by an increase in wafer diameter. The semiconductor industry is converting from 200 millimeter wafer diameters to 300 millimeter wafer diameters.
One component that has a significant impact on the quality of a chemical mechanical planarization process is a translation mechanism. The translation mechanism is a component of a CMP tool that provides movement or translates an apparatus of a chemical mechanical planarization tool from one area to another. For example, unpolished semiconductor wafers are stored in a predetermined area of a CMP tool. A translation mechanism moves a wafer carrier assembly to pick up an unpolished semiconductor wafer. The translation mechanism moves the wafer carrier assembly and the unpolished semiconductor wafer from the unpolished wafer pickup area to a polishing area of the CMP tool. One common type of wafer carrier arm uses cams to produce accurate movement.
The polishing area of a CMP tool typically includes a platen that provides a support structure for a polishing process. In general, the platen is a round metal disk with a flat surface. The platen is rotated to aid in the polishing process. A polishing media is placed on the platen. One type of polishing media is a polyurethane pad. A polyurethane pad is used as a polishing media because it is compliant and provides for the transport of polishing chemistry to a semiconductor wafer during a polishing process.
The translation mechanism accurately moves an exposed surface of the unpolished semiconductor wafer in contact and coplanar to a surface of the polishing media. The semiconductor wafer contacts the polishing media at a predetermined pressure, which partially determines the rate of material removal. The predetermined pressure applied across the surface of the semiconductor wafer, in part, is controlled by the translation mechanism. Typically, pressure to the semiconductor wafer is applied by a combination of translation mechanism induced pressure and gas pressure from the carrier assembly to the back-side of the semiconductor wafer.
Material is removed from the semiconductor wafer by mechanical abrasion and chemical reaction. After completion of the polishing process, the translation mechanism moves the polished semiconductor wafer to a storage area for polished wafers. The quality of polishing is directly related to the control of movement of the translation mechanism.
Pad conditioning during the CMP process also impacts the polishing uniformity across a semiconductor wafer surface. Typically, the polyurethane pad used as the polishing media has grooves or perforations, which aid in the transport of the polishing chemistry. Over time, semiconductor wafer material and spent polishing chemistry become trapped in the polyurethane pad. Trapped particles in the matrix of the polishing media can scratch or modify the polishing process thereby reducing polishing uniformity or worst case, damaging the wafers beyond use. In either case, overall wafer yields are reduced, increasing the cost of manufacture of integrated circuit.
Pad conditioning abrades, planarizes, and removes trapped particulates in the polishing media. Pad conditioning results in a the physical change in the surface of a polyurethane pad (polishing media) that involves abrading and profiling the uppermost surface of the pad. Typically, pad conditioning is achieved by placing a pad conditioner assembly in proximity to the polishing media. An end effector is a component of a pad conditioner assembly that requires contact with the polishing media. The end effector has an abrasive surface that cleans, roughens, and planarizes the surface of the polishing media. A material such as diamond is often used as the abrasive. Typically, the end effector is mounted to a translation mechanism, which brings the end effector in contact with the polishing media. The translation mechanism moves the end effector across the surface of the polishing media to condition the surface of the polishing media. In an embodiment of a CMP tool, both the pad conditioner and the polishing media rotate to increase the effectiveness of the pad conditioning process. In general, pad conditioning is done as often as possible within the constraints imposed by the wafer throughput of the CMP tool.
Problems with prior art translation mechanisms include expensive machining requirements, susceptibility to corrosion, and high maintenance requirements. These problems increase manufacturing costs and reduce reliability of the process and the resultant products.
Accordingly, it would be advantageous to have a translation mechanism for a chemical mechanical planarization tool that has improved reliability in a manufacturing environment. It would be of further advantage for the translation mechanism to reduce the cost of polishing each semiconductor wafer.